Motor vehicle emissions are the leading source of air pollution in most metropolitan areas, causing health, ecological and economical damage. As a result, considerable effort and resources are currently devoted to various emission reduction strategies, such as emission inspection programs, reformulated or alternative fuels, stricter standards for new vehicles, mass transit, improved engine control and catalyst technologies, and upgrade and repair of existing vehicles. However, in order to evaluate the impact of these reduction strategies, it is necessary to measure and collect accurate real-world emission measurements over the life of a vehicle.
Presently, the vast majority of emission tests are performed in a specialized laboratory, where the vehicle is driven on a dynamo meter according to a prescribed driving cycle, such as I/M 240 or FTP for light and medium duty vehicles and CBD for heavy duty vehicles.
This approach has several significant disadvantages: (1) the driving cycles do not adequately represent real-world driving conditions, which vary and are often unknown; (2) vehicles can be optimized for low emissions during the driving cycle, but do not operate optimally in actual use; (3) the testing equipment is bulky and expensive; (4) there are significant costs associated with testing the vehicle, such as vehicle (and/or mobile laboratory) mileage, vehicle downtime, and the test itself, especially on heavy-duty vehicles; (5) individual vehicles engines have unique characteristics which effect emissions, and (6) only a relatively small number of vehicles can be tested.
The first two disadvantages can be eliminated by using a testing system mounted on the vehicle. However, the use of an on-board system is presently limited to repair grade gas analyzers that provide only a rough estimate of mass emissions for repair purposes and a relatively small number of dedicated instrumented vehicles.
For example, it is known that an on-board testing system mounted on a dedicated instrumented vehicle was disclosed by Sierra Research. This system uses a repair-grade four-gas non-dispersive infra-red (NDIR) analyzer to measure exhaust gas concentrations and several sensors mounted on the engine to determine intake air flow. From these measurements, exhaust mass flow and mass emissions can be computed.
A simpler system, using repair grade NDIR analyzer concentration data only, has been developed at the University of Denver to predict I/M 240 mass emissions. Using this system, the average ratio of pollutant to fuel consumed is calculated from the concentration data. The amount of fuel consumed is then estimated from the length of the trip and fuel economy. While this method is successful in predicting whether a vehicle will pass or fail an I/M 240 test, and has been incorporated into newer repair grade analyzers, it is not sufficiently accurate in measuring actual mass emissions, since it does not properly account for emissions during extreme (high or low) exhaust flow. Also, errors in estimating fuel consumption results in the same relative error in mass emission readings.
Accordingly, a system which allows for the testing of individual vehicles during daily operation is necessary to eliminate many of the shortfalls found in the existing systems. One such system was previously disclosed by the inventor. The system employs a five-gas analyzer drawing undiluted exhaust from the tailpipe and calculates mass exhaust flow from engine operating data obtained via a diagnostic link to the computer controlled engine. However, this system can only be employed on engines which include a computerized engine control unit. This greatly limits the number and type of vehicles from which emission measurements may be taken.
Hence, it would be useful to provide a portable mass emissions measuring system which could measure accurate real-world vehicle emissions on a large variety of vehicles without displacing the vehicle from service.